637. Average of Levels in Binary Tree

[Tcdian]

637. Average of Levels in Binary Tree

给定一个非空二叉树, 返回一个由每层节点平均值组成的数组。

Example 1

Input:
    3
   / \
  9  20
    /  \
   15   7
Output: [3, 14.5, 11]
Explanation:
The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].

Note

• 节点值的范围在32位有符号整数范围内。

[Tcdian]

Solution

• JavaScript Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var averageOfLevels = function(root) {
    if (root === null) {
        return [];
    }
    let queue = [[root, 0]];
    const levels = [];
    while (queue.length !== 0) {
        const [node, index] = queue.shift();
        levels[index] = levels[index] || [0, 0];
        levels[index][0] += node.val;
        levels[index][1] += 1;
        if (node.left !== null) {
            queue.push([node.left, index + 1]);
        }
        if (node.right !== null) {
            queue.push([node.right, index + 1]);
        }
    }
    return levels.map(([sum, count]) => sum / count);
};

• TypeScript Solution

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function averageOfLevels(root: TreeNode | null): number[] {
    if (root === null) {
        return [];
    }
    let queue: [TreeNode, number][] = [[root, 0]];
    const levels: [number, number][] = [];
    while (queue.length !== 0) {
        const [node, index] = queue.shift()!;
        levels[index] = levels[index] || [0, 0];
        levels[index][0] += node.val;
        levels[index][1] += 1;
        if (node.left !== null) {
            queue.push([node.left, index + 1]);
        }
        if (node.right !== null) {
            queue.push([node.right, index + 1]);
        }
    }
    return levels.map(([sum, count]) => sum / count);
};